The recent bombings on buses and subways in London have heightened security concerns in the United States. Citizens are being asked to report any suspicious people or activities they see to authorities. Police appear to be searching people who fit a certain racial or ethnic profile, on New York's subways and buses. In the nation's capital, 'Washington, officials are now considering similar searches. Any searches based on racial profiles are the source of much debate.

The recent bombings in London and Egypt, which apparently were carried out by Muslims, have raised Americans' fears of terrorist attacks on United States soil.

At a congressional hearing Tuesday, William Morange, the head of security for the New York City Transit Authority, told lawmakers people's vigilance is crucial to preventing terror attacks, "I really feel that the most important technology that is out there, right there today, is the human element."

But two recent incidents point up the pitfalls of relying people's appearances.

This past weekend, five men, who turned out to be Sikhs from England, were taken off a tour bus in New York City and handcuffed because a worker thought they looked suspicious.

And on Tuesday, a flight from Los Angeles to London was diverted to Boston, because members of the crew thought three Pakistani men were acting strangely. In both cases, the men were targeted because they looked Middle Eastern, but they were completely innocent.

Hussein Ibish of the Progressive Muslim Union says there is a fine line between racial profiling and vigilance. "People should not be considered suspicious because of their race, their ethnicity, their religious affiliation," he said. "That can't be what security policy or behavior boils down to."

Roger Pilon, of the libertarian Washington, DC think tank, the Cato Institute, says it is always a judgment call as to whether racial profiling for security concerns outweighs concerns about people's constitutionally mandated civil liberties. "I suppose it does give some people some sense of comfort, and it is a tricky issue because, on the one hand, you don't want to single out a class of people," he said. "But on the other hand, we know that this terrorism is being done by a relatively clearly identified group of people." But Mr. Pilon also says he thinks there are better ways to combat terrorism, such as intelligence.

For some travelers, like Bill Gardner, some amount of profiling is inevitable when U.S. national security is in question. "I think if they aren't profiling to a certain degree, they aren't doing their job," he said.

Other travelers don't see it quite the same way, like Nadia Haq, who is from Bangladesh. "I get security checks, random security checks, but I don't think they're so random, because my last name is Muslim," she said.

New York's mayor has apologized to the five men who were singled out last weekend, but, he says once police got the report of suspicious people, they no choice but to act.